Re: [PATCH 21/47] drm/i915/guc: Ensure G2H response has space in buffer

[John Harrison <john.c.harrison@intel.com>]

On 7/14/2021 17:06, Matthew Brost wrote:
> On Tue, Jul 13, 2021 at 11:36:05AM -0700, John Harrison wrote:
>> On 6/24/2021 00:04, Matthew Brost wrote:
>>> Ensure G2H response has space in the buffer before sending H2G CTB as
>>> the GuC can't handle any backpressure on the G2H interface.
>>>
>>> Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
>>> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
>>> ---
>>>    drivers/gpu/drm/i915/gt/uc/intel_guc.h        | 13 +++-
>>>    drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c     | 76 +++++++++++++++----
>>>    drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h     |  4 +-
>>>    drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h   |  4 +
>>>    .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 13 ++--
>>>    5 files changed, 87 insertions(+), 23 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc.h b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
>>> index b43ec56986b5..24e7a924134e 100644
>>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc.h
>>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
>>> @@ -95,11 +95,17 @@ inline int intel_guc_send(struct intel_guc *guc, const u32 *action, u32 len)
>>>    }
>>>    #define INTEL_GUC_SEND_NB		BIT(31)
>>> +#define INTEL_GUC_SEND_G2H_DW_SHIFT	0
>>> +#define INTEL_GUC_SEND_G2H_DW_MASK	(0xff << INTEL_GUC_SEND_G2H_DW_SHIFT)
>>> +#define MAKE_SEND_FLAGS(len) \
>>> +	({GEM_BUG_ON(!FIELD_FIT(INTEL_GUC_SEND_G2H_DW_MASK, len)); \
>>> +	(FIELD_PREP(INTEL_GUC_SEND_G2H_DW_MASK, len) | INTEL_GUC_SEND_NB);})
>>>    static
>>> -inline int intel_guc_send_nb(struct intel_guc *guc, const u32 *action, u32 len)
>>> +inline int intel_guc_send_nb(struct intel_guc *guc, const u32 *action, u32 len,
>>> +			     u32 g2h_len_dw)
>>>    {
>>>    	return intel_guc_ct_send(&guc->ct, action, len, NULL, 0,
>>> -				 INTEL_GUC_SEND_NB);
>>> +				 MAKE_SEND_FLAGS(g2h_len_dw));
>>>    }
>>>    static inline int
>>> @@ -113,6 +119,7 @@ intel_guc_send_and_receive(struct intel_guc *guc, const u32 *action, u32 len,
>>>    static inline int intel_guc_send_busy_loop(struct intel_guc* guc,
>>>    					   const u32 *action,
>>>    					   u32 len,
>>> +					   u32 g2h_len_dw,
>>>    					   bool loop)
>>>    {
>>>    	int err;
>>> @@ -121,7 +128,7 @@ static inline int intel_guc_send_busy_loop(struct intel_guc* guc,
>>>    	might_sleep_if(loop && (!in_atomic() && !irqs_disabled()));
>>>    retry:
>>> -	err = intel_guc_send_nb(guc, action, len);
>>> +	err = intel_guc_send_nb(guc, action, len, g2h_len_dw);
>>>    	if (unlikely(err == -EBUSY && loop)) {
>>>    		if (likely(!in_atomic() && !irqs_disabled()))
>>>    			cond_resched();
>>> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
>>> index 7491f041859e..a60970e85635 100644
>>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
>>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
>>> @@ -73,6 +73,7 @@ static inline struct drm_device *ct_to_drm(struct intel_guc_ct *ct)
>>>    #define CTB_DESC_SIZE		ALIGN(sizeof(struct guc_ct_buffer_desc), SZ_2K)
>>>    #define CTB_H2G_BUFFER_SIZE	(SZ_4K)
>>>    #define CTB_G2H_BUFFER_SIZE	(4 * CTB_H2G_BUFFER_SIZE)
>>> +#define G2H_ROOM_BUFFER_SIZE	(PAGE_SIZE)
>> Any particular reason why PAGE_SIZE instead of SZ_4K? I'm not seeing
>> anything in the code that is actually related to page sizes. Seems like
>> '(CTB_G2H_BUFFER_SIZE / 4)' would be a more correct way to express it.
>> Unless I'm missing something about how it's used?
>>
> Yes, CTB_G2H_BUFFER_SIZE / 4 is better.
>
> Matt
Okay. With that changed:

Reviewed-by: John Harrison <John.C.Harrison@Intel.com>


>
>> John.
>>
>>
>>>    struct ct_request {
>>>    	struct list_head link;
>>> @@ -129,23 +130,27 @@ static void guc_ct_buffer_desc_init(struct guc_ct_buffer_desc *desc)
>>>    static void guc_ct_buffer_reset(struct intel_guc_ct_buffer *ctb)
>>>    {
>>> +	u32 space;
>>> +
>>>    	ctb->broken = false;
>>>    	ctb->tail = 0;
>>>    	ctb->head = 0;
>>> -	ctb->space = CIRC_SPACE(ctb->tail, ctb->head, ctb->size);
>>> +	space = CIRC_SPACE(ctb->tail, ctb->head, ctb->size) - ctb->resv_space;
>>> +	atomic_set(&ctb->space, space);
>>>    	guc_ct_buffer_desc_init(ctb->desc);
>>>    }
>>>    static void guc_ct_buffer_init(struct intel_guc_ct_buffer *ctb,
>>>    			       struct guc_ct_buffer_desc *desc,
>>> -			       u32 *cmds, u32 size_in_bytes)
>>> +			       u32 *cmds, u32 size_in_bytes, u32 resv_space)
>>>    {
>>>    	GEM_BUG_ON(size_in_bytes % 4);
>>>    	ctb->desc = desc;
>>>    	ctb->cmds = cmds;
>>>    	ctb->size = size_in_bytes / 4;
>>> +	ctb->resv_space = resv_space / 4;
>>>    	guc_ct_buffer_reset(ctb);
>>>    }
>>> @@ -226,6 +231,7 @@ int intel_guc_ct_init(struct intel_guc_ct *ct)
>>>    	struct guc_ct_buffer_desc *desc;
>>>    	u32 blob_size;
>>>    	u32 cmds_size;
>>> +	u32 resv_space;
>>>    	void *blob;
>>>    	u32 *cmds;
>>>    	int err;
>>> @@ -250,19 +256,23 @@ int intel_guc_ct_init(struct intel_guc_ct *ct)
>>>    	desc = blob;
>>>    	cmds = blob + 2 * CTB_DESC_SIZE;
>>>    	cmds_size = CTB_H2G_BUFFER_SIZE;
>>> -	CT_DEBUG(ct, "%s desc %#tx cmds %#tx size %u\n", "send",
>>> -		 ptrdiff(desc, blob), ptrdiff(cmds, blob), cmds_size);
>>> +	resv_space = 0;
>>> +	CT_DEBUG(ct, "%s desc %#tx cmds %#tx size %u/%u\n", "send",
>>> +		 ptrdiff(desc, blob), ptrdiff(cmds, blob), cmds_size,
>>> +		 resv_space);
>>> -	guc_ct_buffer_init(&ct->ctbs.send, desc, cmds, cmds_size);
>>> +	guc_ct_buffer_init(&ct->ctbs.send, desc, cmds, cmds_size, resv_space);
>>>    	/* store pointers to desc and cmds for recv ctb */
>>>    	desc = blob + CTB_DESC_SIZE;
>>>    	cmds = blob + 2 * CTB_DESC_SIZE + CTB_H2G_BUFFER_SIZE;
>>>    	cmds_size = CTB_G2H_BUFFER_SIZE;
>>> -	CT_DEBUG(ct, "%s desc %#tx cmds %#tx size %u\n", "recv",
>>> -		 ptrdiff(desc, blob), ptrdiff(cmds, blob), cmds_size);
>>> +	resv_space = G2H_ROOM_BUFFER_SIZE;
>>> +	CT_DEBUG(ct, "%s desc %#tx cmds %#tx size %u/%u\n", "recv",
>>> +		 ptrdiff(desc, blob), ptrdiff(cmds, blob), cmds_size,
>>> +		 resv_space);
>>> -	guc_ct_buffer_init(&ct->ctbs.recv, desc, cmds, cmds_size);
>>> +	guc_ct_buffer_init(&ct->ctbs.recv, desc, cmds, cmds_size, resv_space);
>>>    	return 0;
>>>    }
>>> @@ -458,7 +468,7 @@ static int ct_write(struct intel_guc_ct *ct,
>>>    	/* now update descriptor */
>>>    	ctb->tail = tail;
>>>    	WRITE_ONCE(desc->tail, tail);
>>> -	ctb->space -= len + 1;
>>> +	atomic_sub(len + 1, &ctb->space);
>>>    	return 0;
>>> @@ -521,13 +531,34 @@ static inline bool ct_deadlocked(struct intel_guc_ct *ct)
>>>    	return ret;
>>>    }
>>> +static inline bool g2h_has_room(struct intel_guc_ct *ct, u32 g2h_len_dw)
>>> +{
>>> +	struct intel_guc_ct_buffer *ctb = &ct->ctbs.recv;
>>> +
>>> +	/*
>>> +	 * We leave a certain amount of space in the G2H CTB buffer for
>>> +	 * unexpected G2H CTBs (e.g. logging, engine hang, etc...)
>>> +	 */
>>> +	return !g2h_len_dw || atomic_read(&ctb->space) >= g2h_len_dw;
>>> +}
>>> +
>>> +static inline void g2h_reserve_space(struct intel_guc_ct *ct, u32 g2h_len_dw)
>>> +{
>>> +	lockdep_assert_held(&ct->ctbs.send.lock);
>>> +
>>> +	GEM_BUG_ON(!g2h_has_room(ct, g2h_len_dw));
>>> +
>>> +	if (g2h_len_dw)
>>> +		atomic_sub(g2h_len_dw, &ct->ctbs.recv.space);
>>> +}
>>> +
>>>    static inline bool h2g_has_room(struct intel_guc_ct *ct, u32 len_dw)
>>>    {
>>>    	struct intel_guc_ct_buffer *ctb = &ct->ctbs.send;
>>>    	u32 head;
>>>    	u32 space;
>>> -	if (ctb->space >= len_dw)
>>> +	if (atomic_read(&ctb->space) >= len_dw)
>>>    		return true;
>>>    	head = READ_ONCE(ctb->desc->head);
>>> @@ -540,16 +571,16 @@ static inline bool h2g_has_room(struct intel_guc_ct *ct, u32 len_dw)
>>>    	}
>>>    	space = CIRC_SPACE(ctb->tail, head, ctb->size);
>>> -	ctb->space = space;
>>> +	atomic_set(&ctb->space, space);
>>>    	return space >= len_dw;
>>>    }
>>> -static int has_room_nb(struct intel_guc_ct *ct, u32 len_dw)
>>> +static int has_room_nb(struct intel_guc_ct *ct, u32 h2g_dw, u32 g2h_dw)
>>>    {
>>>    	lockdep_assert_held(&ct->ctbs.send.lock);
>>> -	if (unlikely(!h2g_has_room(ct, len_dw))) {
>>> +	if (unlikely(!h2g_has_room(ct, h2g_dw) || !g2h_has_room(ct, g2h_dw))) {
>>>    		if (ct->stall_time == KTIME_MAX)
>>>    			ct->stall_time = ktime_get();
>>> @@ -563,6 +594,9 @@ static int has_room_nb(struct intel_guc_ct *ct, u32 len_dw)
>>>    	return 0;
>>>    }
>>> +#define G2H_LEN_DW(f) \
>>> +	FIELD_GET(INTEL_GUC_SEND_G2H_DW_MASK, f) ? \
>>> +	FIELD_GET(INTEL_GUC_SEND_G2H_DW_MASK, f) + GUC_CTB_HXG_MSG_MIN_LEN : 0
>>>    static int ct_send_nb(struct intel_guc_ct *ct,
>>>    		      const u32 *action,
>>>    		      u32 len,
>>> @@ -570,12 +604,13 @@ static int ct_send_nb(struct intel_guc_ct *ct,
>>>    {
>>>    	struct intel_guc_ct_buffer *ctb = &ct->ctbs.send;
>>>    	unsigned long spin_flags;
>>> +	u32 g2h_len_dw = G2H_LEN_DW(flags);
>>>    	u32 fence;
>>>    	int ret;
>>>    	spin_lock_irqsave(&ctb->lock, spin_flags);
>>> -	ret = has_room_nb(ct, len + 1);
>>> +	ret = has_room_nb(ct, len + 1, g2h_len_dw);
>>>    	if (unlikely(ret))
>>>    		goto out;
>>> @@ -584,6 +619,7 @@ static int ct_send_nb(struct intel_guc_ct *ct,
>>>    	if (unlikely(ret))
>>>    		goto out;
>>> +	g2h_reserve_space(ct, g2h_len_dw);
>>>    	intel_guc_notify(ct_to_guc(ct));
>>>    out:
>>> @@ -965,10 +1001,22 @@ static void ct_incoming_request_worker_func(struct work_struct *w)
>>>    static int ct_handle_event(struct intel_guc_ct *ct, struct ct_incoming_msg *request)
>>>    {
>>>    	const u32 *hxg = &request->msg[GUC_CTB_MSG_MIN_LEN];
>>> +	u32 action = FIELD_GET(GUC_HXG_EVENT_MSG_0_ACTION, hxg[0]);
>>>    	unsigned long flags;
>>>    	GEM_BUG_ON(FIELD_GET(GUC_HXG_MSG_0_TYPE, hxg[0]) != GUC_HXG_TYPE_EVENT);
>>> +	/*
>>> +	 * Adjusting the space must be done in IRQ or deadlock can occur as the
>>> +	 * CTB processing in the below workqueue can send CTBs which creates a
>>> +	 * circular dependency if the space was returned there.
>>> +	 */
>>> +	switch (action) {
>>> +	case INTEL_GUC_ACTION_SCHED_CONTEXT_MODE_DONE:
>>> +	case INTEL_GUC_ACTION_DEREGISTER_CONTEXT_DONE:
>>> +		atomic_add(request->size, &ct->ctbs.recv.space);
>>> +	}
>>> +
>>>    	spin_lock_irqsave(&ct->requests.lock, flags);
>>>    	list_add_tail(&request->link, &ct->requests.incoming);
>>>    	spin_unlock_irqrestore(&ct->requests.lock, flags);
>>> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h
>>> index 9924335e2ee6..660bf37238e2 100644
>>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h
>>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h
>>> @@ -33,6 +33,7 @@ struct intel_guc;
>>>     * @desc: pointer to the buffer descriptor
>>>     * @cmds: pointer to the commands buffer
>>>     * @size: size of the commands buffer in dwords
>>> + * @resv_space: reserved space in buffer in dwords
>>>     * @head: local shadow copy of head in dwords
>>>     * @tail: local shadow copy of tail in dwords
>>>     * @space: local shadow copy of space in dwords
>>> @@ -43,9 +44,10 @@ struct intel_guc_ct_buffer {
>>>    	struct guc_ct_buffer_desc *desc;
>>>    	u32 *cmds;
>>>    	u32 size;
>>> +	u32 resv_space;
>>>    	u32 tail;
>>>    	u32 head;
>>> -	u32 space;
>>> +	atomic_t space;
>>>    	bool broken;
>>>    };
>>> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h b/drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h
>>> index 4e4edc368b77..94bb1ca6f889 100644
>>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h
>>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_fwif.h
>>> @@ -17,6 +17,10 @@
>>>    #include "abi/guc_communication_ctb_abi.h"
>>>    #include "abi/guc_messages_abi.h"
>>> +/* Payload length only i.e. don't include G2H header length */
>>> +#define G2H_LEN_DW_SCHED_CONTEXT_MODE_SET	2
>>> +#define G2H_LEN_DW_DEREGISTER_CONTEXT		1
>>> +
>>>    #define GUC_CONTEXT_DISABLE		0
>>>    #define GUC_CONTEXT_ENABLE		1
>>> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>>> index 010e46dd6b16..ef24758c4266 100644
>>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>>> @@ -260,6 +260,7 @@ static int guc_add_request(struct intel_guc *guc, struct i915_request *rq)
>>>    	struct intel_context *ce = rq->context;
>>>    	u32 action[3];
>>>    	int len = 0;
>>> +	u32 g2h_len_dw = 0;
>>>    	bool enabled = context_enabled(ce);
>>>    	GEM_BUG_ON(!atomic_read(&ce->guc_id_ref));
>>> @@ -271,13 +272,13 @@ static int guc_add_request(struct intel_guc *guc, struct i915_request *rq)
>>>    		action[len++] = GUC_CONTEXT_ENABLE;
>>>    		set_context_pending_enable(ce);
>>>    		intel_context_get(ce);
>>> +		g2h_len_dw = G2H_LEN_DW_SCHED_CONTEXT_MODE_SET;
>>>    	} else {
>>>    		action[len++] = INTEL_GUC_ACTION_SCHED_CONTEXT;
>>>    		action[len++] = ce->guc_id;
>>>    	}
>>> -	err = intel_guc_send_nb(guc, action, len);
>>> -
>>> +	err = intel_guc_send_nb(guc, action, len, g2h_len_dw);
>>>    	if (!enabled && !err) {
>>>    		set_context_enabled(ce);
>>>    	} else if (!enabled) {
>>> @@ -730,7 +731,7 @@ static int __guc_action_register_context(struct intel_guc *guc,
>>>    		offset,
>>>    	};
>>> -	return intel_guc_send_busy_loop(guc, action, ARRAY_SIZE(action), true);
>>> +	return intel_guc_send_busy_loop(guc, action, ARRAY_SIZE(action), 0, true);
>>>    }
>>>    static int register_context(struct intel_context *ce)
>>> @@ -750,7 +751,8 @@ static int __guc_action_deregister_context(struct intel_guc *guc,
>>>    		guc_id,
>>>    	};
>>> -	return intel_guc_send_busy_loop(guc, action, ARRAY_SIZE(action), true);
>>> +	return intel_guc_send_busy_loop(guc, action, ARRAY_SIZE(action),
>>> +					G2H_LEN_DW_DEREGISTER_CONTEXT, true);
>>>    }
>>>    static int deregister_context(struct intel_context *ce, u32 guc_id)
>>> @@ -889,7 +891,8 @@ static void __guc_context_sched_disable(struct intel_guc *guc,
>>>    	intel_context_get(ce);
>>> -	intel_guc_send_busy_loop(guc, action, ARRAY_SIZE(action), true);
>>> +	intel_guc_send_busy_loop(guc, action, ARRAY_SIZE(action),
>>> +				 G2H_LEN_DW_SCHED_CONTEXT_MODE_SET, true);
>>>    }
>>>    static u16 prep_context_pending_disable(struct intel_context *ce)